(i) Field of the Invention
The present invention relates to image read apparatuses such as a scanner, FAX, copy machine, and complex machine using an image sensor on which one-dimensionally arranged light receiving devices are mounted to read an image of a draft as electronic data.
(ii) Description of the Related Art
Image read apparatuses such as a scanner, FAX, copy machine, and complex machine have heretofore been known using an image sensor on which one-dimensionally arranged light receiving devices are mounted to read an image of a draft as electronic data.
Additionally, in the reading of the image in the image read apparatus, for example, even a photo image having a large data amount is to be read with high precision, the data amount of the image read with the good precision is to be reduced for use in transferring the data via FAX, a large amount of drafts is to be read as fast as possible even if an image quality drops, or the image is to be read with an acceptable image quality and data amount. In this manner, the desired way of reading the image data varies in accordance with the use application of the read image and situations at a read time.
On the other hand, the resolution of the read image data has heretofore been increased/decreased in outputting the data, so that the image quality and data amount are changed to handle various applications.
Moreover, as one of the methods for solving the problem, for various uses, as shown in FIG. 2, a CCD linear image sensor has been developed. The sensor includes: two sensors (first sensor 21, second sensor 22) including a plurality of light receiving devices arranged in a main scanning direction; a first shift register 25 for outputting pixel signals (17 signals in the example of FIG. 2) of all the light receiving devices of the first sensor 21; a second shift register 26 for outputting even-numbered pixel signals (eight signals in the example of FIG. 2) of the light receiving devices of the second sensor 22; and a third shift register 27 for outputting odd-numbered pixel signals (nine signals in the example of FIG. 2) of the light receiving devices of the second sensor 22.
On the other hand, for the transmission of the pixel signals from this CCD image sensor, electric charges accumulated in the light receiving devices are successively outputted as the pixel signals by the shift register. When the outputs from the three shift registers are simultaneously outputted, there is a shift register in which the pixel signals fast run out. This is because the number of pixel signals outputted from each shift register is different. However, the outputs from three shift registers are usually controlled in one system. Therefore, while there is even one shift register in which the pixel signals to be outputted are left, the output operation of the pixel signals continues. Therefore, even the shift register in which the pixel signals run out undergoes the operation for outputting the pixel signals, and invalid data is transmitted and recorded in a memory.
In a conventional image read apparatus, as shown in FIG. 15, the pixel signal read by a CCD linear image sensor (hereinafter referred to as the CCD sensor 20) which is the above-described CCD linear image sensor is selected by a selector 76. An A/D converter 77 converts the signal into a digital signal (pixel data), a data sampling block 44 in an image read control section 40 receives pixel data, and a memory interface circuit 46 in the image read control section 40 writes the pixel data into a memory 70. In the image read apparatus constituted in this manner, the pixel signals are transmitted as follows.
First, in the CCD sensor 20, as shown in FIG. 3, voltages are outputted to output terminals OUT1 to OUT3 in accordance with the electric charges transferred from the shift registers for each edge of transfer clocks φ1, φ2. That is, the pixel signal of the image received by the light receiving device is outputted. At this time, pixel information is not included in ninth and subsequent edges of the transfer clock for the second shift register, and is not included in tenth and subsequent signals for the third shift register.
Next, the pixel signal outputted from the CCD sensor 20 is received by the selector 76, and the pixel signals of three channels received by the selector 76 are selected in order and outputted to the A/D converter 77 within period of the transfer clocks φ1, φ2 as shown in FIG. 4A. In the A/D converter 77, an analog signal is converted to a digital signal and outputted as a serial data string in the same period as that of the output of the selector 76 as shown in FIG. 4B.
At this time, the outputs from the second shift register in the ninth and subsequent edges of the transfer clock and the outputs from the third shift register in the tenth and subsequent edges do not include pixel information, but the selector 76 selects the channels of the second and third shift registers in the case where the outputs from those channels do not include pixel information. Therefore, the A/D converter 77 carries out the operation for forming the digital signal even with respect to the channels which do not include the pixel information, and the signals are transmitted as the serial data string (hatched part of FIGS. 4A and 4B), and recorded in the memory as shown in FIG. 5A.
In this manner, the invalid data which does not include the pixel information uses a memory region, and there is a problem that a memory capacity is compressed. Moreover, the invalid data is included at the time of image processing using the pixel data recorded in the memory. There is another problem that it takes time to read the data from the memory and a process of selecting the invalid data is required in the stage of the image processing.
Additionally, in the normal CCD image sensor, light receiving ends have many manufacturing problems of the light receiving device and many eclipses of an optical system. Moreover, it is impossible to obtain an output with a stably high precision from the light receiving ends. For these reasons, the signals from the opposite ends of the given range of a light receiving device string are not regarded as valid, the light receiving device in the middle part of the light receiving device string is defined as valid pixels, and the signals from this range of the valid pixels are used as the pixel signal obtained by picking up the image of a subject.
However, the outputs from the CCD image sensor are outputted in order from the signal of the endmost light receiving device, and the signals other than the valid pixels (i.e., invalid pixels) are outputted in the same manner as the valid pixels.
Therefore, the signals of the invalid pixels are written in the memory in the same manner as the signals of the valid pixels. Moreover, the invalid pixels are selected so that the invalid pixels are not used in the stage of the image processing using the read pixel signal.
Therefore, the data of the invalid pixels uses the memory region, and there is a problem that the memory capacity is compressed. Moreover, the invalid data is included in the image processing using the read data, and therefore the data to be processed increases. There is another problem that it takes time to read the data and to select the invalid pixel data.
Especially, in the above-described CCD image sensor including two rows of sensors and having three outputs, there are invalid pixels for two sensors, and therefore the number of invalid pixels is large with respect to the outputs from one sensor. Moreover, with three simultaneous outputs, the second and third shift registers start to output the valid pixels before the pixels of the first shift register become valid. Therefore, the data of valid and invalid pixels are mixed and recorded (stored). When the read image data is subjected to the image processing later, the efficiency of the selection process of the information is bad.
For example, as shown in FIG. 9, the valid pixels of the light receiving devices in the first and second sensors 21 and 22 in the CCD linear image sensor correspond to nine pixels including the seventh to 15th pixels from an output end direction. A take-in start pixel in the first shift register 25 corresponds to the seventh pixel from the output end direction and the number of taken pixels is nine. The take-in start pixel in the second shift register 26 corresponds to the fourth pixel from the output end direction and the number of taken pixels is four. The take-in start pixel in the third shift register 27 corresponds to the fourth pixel from the output end direction and the number of taken pixels is five. In this case, when the output of the pixel signal from the CCD linear image sensor is recorded (stored) in the memory as such, as shown in FIG. 11A, the data of the valid pixels (part without hatching of FIG. 11A) is mixed with the data of the invalid pixels (hatched part of FIG. 11A) and recorded (stored).
In this CCD linear image sensor includes two rows of sensors and having three outputs, the influence of the invalid pixels is large, and raises a problem. This problem also occurs also in reading only a part of the draft in a main scanning direction as an object.